leaching of titaniferous materials

ABSTRACT

A process for facilitating removal of one or more impurities from titaniferous material containing the impurities in a form which is highly soluble in acid. The material is in turn leached with a sulphuric acid solution and with a hydrochloric acid solution in either order. To enhance the susceptibility of the impurities to removal, the hydrochloric acid leach is augmented by one or more of the following: (i) addition of an effective amount of an added chloride salt; (ii) pre-treatment of the titaniferous material with a solution of an effective amount of a carbonate salt, preferably an alkali metal or alkaline earth metal carbonate; and/or (iii) pre-treatment of the titaniferous material with a solution of an effective amount of a hydroxide, preferably an alkali metal or alkaline earth metal hydroxide.

FIELD OF THE INVENTION

This invention relates to a process for facilitating the removal ofimpurities, especially but not only radionuclides such as uranium andthorium and their radionuclide daughters, from titaniferous materials,and is concerned in particular embodiments with the removal ofimpurities, including especially uranium and thorium, from productsformed from weathered or "altered" ilmenite.

BACKGROUND ART

Ilmenite (FeTiO₃) and rutile (TiO₂) are the major,commercially-important, mineral feedstocks for titanium metal andtitanium dioxide production and generally occur together in nature ascomponents of "mineral sands" or "heavy minerals", along with zircon(ZrSiO₄) and monazite ((Ce, La, Th)PO₄). Natural weathering of ilmeniteresults in partial oxidation of the iron, originally present in ilmenitein the ferrous state (Fe²⁺), to ferric iron (Fe³⁺). To maintainelectrical neutrality, some of the oxidised iron must be removed fromthe ilmenite lattice. This results in a more porous structure with ahigher titanium (lower iron) content. Such weathered materials are knownas "altered" ilmenites and may have TiO₂ contents in excess of 60% TiO₂,compared with 52.7% TiO₂ in stoichiometric (unaltered) ilmenite. Asweathering, or alteration, of the ilmenite proceeds, impurities such asalumino-silicates (clays) are often incorporated into the porousstructure as discrete, small grains that reside in the pores of thealtered ilmenite. It appears that uranium and thorium can also beincorporated into the ilmenite during this process.

Most of the world's mined ilmenite is used for the production oftitanium dioxide pigments for use in the paint and paper industries.Pigment-grade titania (titanium dioxide, TiO₂) has been traditionallyproduced by reacting ilmenite with concentrated sulphuric acid andsubsequent processing to produce a TiO₂ pigment--the so-called sulphateroute. However, this process is becoming increasingly undesirable onenvironmental grounds due to the large volumes of acidic liquid wasteswhich it produces. The alternative process--the so-called chlorideroute--involves reaction with chlorine to produce volatile titaniumtetrachloride (TiCl₄) and subsequent conversion to TiO₂ . Unlike thesulphate route, the chloride route is capable of handling feedstocks,such as rutile, which are high in TiO₂ content and low in iron and otherimpurities. Consequently the chloride-route presents fewer environmentalproblems and has become the preferred method for TiO₂ pigmentproduction. Natural rutile supplies are insufficient to meet the worlddemands of the chloride-route. Thus, there is an increasing need toconvert the more-plentiful ilmenites and altered ilmenites (typically 45to 65% TiO₂) to synthetic rutile (containing over 90% TiO₂). A number ofdifferent processes have been developed to upgrade ilmenite to syntheticrutile, the most widely used, commercially, being the Becher process.

The Becher process involves the following main stages.

1. Reduction, in a rotary kiln, of the iron oxides contained in theilmenite feed largely to metallic iron, at temperatures in the range900°-1200° C., using coal as the heat source and the reductant. Theprincipal product is known as reduced ilmenite (RI).

2. Cooling, in an oxygen-free environment, the solids discharging fromthe reduction kiln.

3. Dry physical separation of the reduced ilmenite and surplus char.

4. Aqueous oxidation (known as aeration) of the reduced ilmenite toconvert the metallic iron to iron oxide particles discrete from the TiO₂-rich mineral particles.

5. Wet physical separation to remove the iron oxides from the TiO₂ -richmineral. Hereinafter the product of this step is referred to as "aeratedproduct".

6. An optional leaching stage to remove a portion of the residual ironand some manganese and magnesium.

7. Washing, dewatering and drying of the synthetic rutile product.

Whether ilmenite is marketed as the raw mineral or as upgraded,value-added, synthetic rutile, producers are being increasingly requiredto meet more stringent limits for radioactivity levels in theirproducts. To meet the limits requires the removal of uranium and thoriumand their radionuclide daughters from the material. The Becher syntheticrutile process does not reduce significantly the levels of uranium andthorium in the product and so there has been an increasing need todevelop an economic and effective process for removal of uranium andthorium, and the associated radionuclide daughters, from ilmenite andother titaniferous materials (eg synthetic rutile).

Frequently ilmenite concentrates contain low levels of thorium due tomonazite contamination. It is not a purpose of this invention, in itsapplication to radionuclide impurities, to remove macroscopic monazitegrains from titaniferous materials, but rather to remove the microscopicuranium and thorium originally incorporated into the ilmenite grainsduring the weathering process.

U.S. Pat. Nos. 5,011,666 and 5,085,837 disclose a process for removingthorium and uranium, and other impurities, from TiO₂ ore by subjectingthe ore to two or more leaching treatments, the said leaching treatmentsalternating between the use of an aqueous solution of mineral acid,preferably hydrochloric acid, and an aqueous solution of an alkali metalcarbonate, hydroxide or mixtures thereof, most preferably sodiumhydroxide. The acid leach occurs first in the claims of U.S. Pat. No.5,011,666, and second in U.S. Pat. No. 5,085,837. The leaches may beseparated by an intervening filtration and wash. Example III in eachpatent discloses a three-step leach with hydrochloric acid, then sodiumhydroxide, then hydrochloric acid. The NaOH leach is exemplified atconcentrations of 20 and 30% (5M and 7.5M respectively), and at atemperature of 160° C. to 210° C. and 8 to 18 atm pressure. These arevery high pressures which we consider would be very expensive andperhaps even technically not feasible. The HCl acid leaches areexemplified at 20% (5.5M). Roasting at a temperature of less than about700° C. prior to the leaching treatment is proposed for some ores.Analytical data in the patent is considered to be by conventionalanalytical methods such as x-ray fluorescence spectrometry. Thistechnique only measures the concentration of the parent thorium anduranium isotopes in the sample and does not give any indication of theconcentration of their radionuclide daughters. Radionuclide measuringtechniques (such as gamma-spectroscopy) are required to measure theconcentrations of the daughter isotopes.

The present applicant's prior Australian patent application 14981/92discloses a process for facilitating removal of radionuclides fromtitaniferous material in which the latter is subjected to a treatmentwith an aqueous solution of an alkali metal oxide or hydroxide at asolution temperature preferably no greater than 125° C., and thereafterleached with mineral acid, preferably sulphuric acid. It was found thatthis process did result in the recovery of significant thorium but didnot correspondingly reduce radioactivity.

The present applicant's Australian patent application no. 14980/92discloses a process for treating titaniferous material to remove thoriumand/or uranium in which the material is leached with acid with addedfluoride.

International Patent Publication WO94/03647 (PCT/AU93/00381), by thepresent applicant, discloses the discovery that while leaching, androasting and leaching, treatments (such as those disclosed in AU14981/92, U.S. Pat. No. 5,085,837 and U.S. Pat. No. 5,011,666) mayremove the parent thorium isotope (²³² Th), the radionuclide decayproducts, or "daughters", in particular ²²⁸ Ra and ²²⁸ Th, are notremoved to the same extent. As a consequence the radioactivity levels ofthe leached materials are higher than expected from the assay value forthe parent isotope and may be too high to meet the radioactivity limitfor the product. International Patent Publication WO94/03647 teachesthat removal of the parent thorium isotope and its radionuclidedaughters occur together when the material is heated (roasted) at atemperature of 1000° C. prior to leaching but then the amount of thoriumremoved is less than that achieved without heating or after heating atup to 500° C. Only by heating at 1400° C. does the subsequent leachingresult in removal of thorium and associated radionuclide daughterstogether, and to the same extent as when the heating temperatures is500° C. or lower. However, heating at 1400° C. prior to leaching is notexpected to be an economic process.

U.S. Pat. No. 5,181,956 discloses an acid leaching step to removeimpurities, including uranium and thorium, from titaniferous orescomprising contacting the ore with an aqueous solution of a mineral acidhaving a concentration of about 3-30 wt % at a temperature of about160°-300° C. Again the expectation, based on the teaching ofInternational Patent Application WO94/03647, is that leaching the ore,even at 300° C., may remove the parent thorium isotope but does notremove the radionuclide daughters, and so lower the activity level ofthe sample, to the degree indicated by the analysis value of the parentthorium isotope.

Optionally, U.S. Pat. No. 5,181,956 discloses that the ore may be givena reductive roast, preferably at 1100°-1300° C., before leaching. Noexamples of the effect of a reductive roast prior to leaching on theremoval of thorium are given in U.S. Pat. No. 5,181,956. While theparent thorium and radionuclide daughters can be expected to be removedto a similar extent after such a reductive roast, current work, asdescribed in examples to this patent, have shown that the extent towhich the parent isotope is removed is much less than when the ore isleached without the reductive roast before leaching.

Australian patent 599090 discloses a process for purifying TiO₂ ore inwhich the ore is roasted, eg at 600° C. to 1100° C., with an alkalimetal compound, which may be inter alia a carbonate or hydroxide, toconvert impurities including thorium and uranium into an acid solubleform, which is then leached with a solution of a non-sulphuric mineralacid, eg hydrochloric acid.

The aforementioned International Patent Publication WO94/03647 furtherdiscloses a process for facilitating the removal of impurities,including radionuclides, from titaniferous material which comprisestreating the titaniferous material to cause aggregation or concentrationof the radionuclides to an extent effective to enhance the accessibilityof the radionuclides to subsequent removal. The radionuclides may beuranium and/or thorium and/or one or more of their radionuclidedaughters. The treatment preferably includes heating the titaniferousmaterial while contacting it with one or more reagents. Particularlyeffective reagents, in that they achieved optimum incorporation of theradionuclides, include alkali and alkaline earth borates. The processoptionally includes treatment of the heated treated titaniferousmaterial directly with an acid leach, or with an acid leach afteraeration, to dissolve the phase incorporating the impurities includingthe radionuclides and thereby to extract them from the titaniferousmaterial. The titaniferous material used in the process may be, eg,ilmenite or altered ilmenite, reduced ilmenite, or synthetic rutile.

In the preferred treatment, the reagents selected for the treatment areknown to melt as a result of a heat treatment and are glass formingagents. They form a liquid phase which disperses onto the surfaces ofthe titaniferous material, and in so doing, collects and concentratesthe impurities including radionuclides and/or one or more daughters. Incooling the titaniferous material prior to acid leaching, the phasecontaining the radionuclides is thought likely to form a glassy phasecontaining the radionuclides. From the known solubility of glassesexpected to form in the system it is anticipated that the glassy phasewould be dissolved during the acid leach. The acid leaches disclosed inthe international application are a single hydrochloric acid leach of aleast 0.05M, or a sulphuric acid leach followed by a hydrochloric acidleach. In some examples, the single hydrochloric acid leach containssodium fluoride.

Other disclosures concerned with or embracing radioactivity reduction inheavy mineral concentrates and/or mineral sands ores includeInternational Patent Publications WO92/18985, WO94/04709 and WO94/05015and Australian Patent Application 44589/93.

DISCLOSURE OF THE INVENTION

A difficulty encountered with the leaching systems disclosed inWO94/03647 is that removal of the radium, a radionuclide decay productor daughter of thorium, tends to be less effective than desired, atleast for economically optimum strengths of hydrochloric acid. It is anobject of the present invention, in its application to the removal ofradionuclide impurities, to at least in part alleviate this problem.

In accordance with a preferred embodiment of the invention, it has nowbeen found that the phase containing the radionuclides formed fromtitaniferous material according to WO94/03647 can be leached andextracted from the material by leaching systems other than thosedisclosed previously. These new systems are also likely to be morecost-effective as a result of the lower reagent concentrations generallyrequired for a given level of impurity, especially radionuclide,removal.

In particular, in accordance with one aspect of the invention,titaniferous material containing one or more impurities in a form whichis highly soluble in acid is in turn leached with a sulphuric acidsolution and with a hydrochloric acid solution in either order, andwherein the hydrochloric acid leach is augmented by one or more of thefollowing:

(i) addition of an effective amount of an added chloride salt;

(ii) pre-treatment of the titaniferous material with a solution of aneffective amount of a carbonate salt, preferably an alkali metal oralkaline earth metal carbonate or; and or

(iii) pre-treatment of the titaniferous material with a solution of aneffective amount of a hydroxide, preferably an alkali metal or alkalineearth metal hydroxide;

whereby to enhance the susceptibility of the impurities to removal.

In another aspect, the invention provides a process for facilitatingremoval of one or more impurities including radionuclides and theirdaughters from titaniferous material containing the impurities in aphase formed by contacting a titaniferous material at an elevatedtemperature with one or more reagents selected to form the phase at theelevated temperature, which phase disperses onto the surfaces of thetitaniferous material and incorporates the impurities;

wherein the material is in turn leached with a mineral acid solution andwith a hydrochloric acid solution in either order, wherein thehydrochloric acid leach is augmented by a pre-treatment with a solutionof an effective amount of an alkali metal hydroxide at a concentrationno greater than 0.01M, preferably in the range 0.005 to 0.01M, atemperature in the range ambient to 80° C., and a pressure in the range1 to 5 atmospheres;

whereby to enhance the susceptibility of the impurities including theradionuclides and their daughters to removal.

By "either order" in case (ii) and (iii) is meant that the sulphuricacid leach may either precede the carbonate or hydroxide pre-treatmentor follow the hydrochloric acid leach of the pre-treated titaniferousmaterial.

Of the three principal alternatives at (i), (ii) and (iii),pre-treatment with hydroxide is usually the preferred approach, but thismay depend on the overall conditions and on the impurities of particularinterest.

In all these alternative systems, the products of the leaches, ortreatments, are typically washed and may be dried before the next step.Plural washes may be desirable for each washing step.

EMBODIMENTS OF THE INVENTION

In general, the titaniferous material is selected from the groupincluding ilmenite, altered ilmenite, reduced ilmenite and syntheticrutile. Conveniently, the synthetic rutile may be in the form of aeratedproduct formed by treatment of ilmenite, which treatment includesreduction of iron therein largely to metallic iron and then aqueousoxidation of the metallic iron to form a separable iron oxide. The formof the impurities which is highly soluble in acid may be a phase inwhich the impurities have been incorporated, for example by the processdisclosed in WO94/03647 (PCT/AU93/00381). Especially effective fortreatment according to the present invention is a phase formed bycontacting a titaniferous material at an elevated temperature, forexample during reduction of iron in ilmenite, with one or more reagentsselected to form the phase at the elevated temperature which phasedisperses onto the surfaces of the titaniferous material andincorporates the impurities. The elevated temperature is preferably inthe range 900° to 1200° C., more preferably 1050° C. to 1200° C.Preferred such reagents include glass forming reagents, especiallyborates such as alkali metal and alkaline earth metal borates. A reagentmixture may be utilised containing two or more such reagents.

In general the impurities removed may be one or more of the groupconsisting of silicon and/or silica, aluminium and/or alumina,manganese, residual iron, calcium, thorium and uranium. The process isespecially useful in the case where the impurities removed includeradionuclides such as uranium, thorium and one or more of theirradionuclide daughters including radium, for example thorium as ²³² Thand its daughters ²²⁸ Th and ²²⁸ Ra.

The titaniferous material may be treated aerated product (ashereinbefore defined) which has been produced from a Becher process inwhich the reduction step (1) includes treatment in accordance with aprocess as disclosed in WO94/03647, eg addition of a reagent to form aphase incorporating impurities including radionuclides for said leachingin accordance with the invention.

Preferred reagents include sodium chloride as the chloride salt, sodiumcarbonate as the alkali metal carbonate, and sodium hydroxide as thealkali metal hydroxide. In the treatment systems the sulphuric acid maybe between 0.1M and 5M, the hydrochloric acid between 0.01 and 3M, thesodium chloride between 0.05 and 5M, the sodium carbonate between 0.01and 1M, and the sodium hydroxide between 0.001 and 10M, more preferablyno greater than 1M. These concentrations refer to the actual aqueoussolution which is contacted with the titaniferous material.

Preferably, where the sulphuric acid leach precedes the hydrochloricacid leach, the concentration of sulphuric acid is selected to be inexcess to the extent that free acid is present after the leach, wherebyto reduce the effective concentration of the hydrochloric acid foroptimum impurity removal.

In general, it is found that, where the impurity is thorium and itsdaughters, overall radionuclide, especially radium, removal andaccordingly radioactivity reduction, are enhanced for a givenhydrochloric acid concentration, and that specific levels ofradionuclide removal and radioactivity reduction can therefore beachieved more economically. It is thought that, possibly, added chlorideor pre-treatment with carbonate or hydroxide, may be effective inselectively taking up the radium as acid soluble radium chloride or byforming an acid soluble carbonate or acid soluble oxide/hydroxide,respectively.

The treatment may be carried out with suspensions of the treatedtitaniferous material at a solids pulp density of between 5 and 70 wt %solids, a temperature ambient to 95° C., a pressure from 1 to 5atmospheres and for up to 4 hours.

The preferred leaching conditions for the sulphuric acid leach are attemperatures up to 80° C. and a pressure of 1 to 5 atmospheres and forup to 2 hours. The preferred conditions for the hydrochloric acid leachare at temperatures of up to 60° C., a pressure of 1 to 5 atmospheresand leach times of 2 hours, and more preferably greater than 2 minutesbut less than 30 minutes at a solids pulp density of 30 wt % solids orhigher. The preferred conditions for the sodium hydroxide leach are atemperature in the range ambient up to 80° C., a pressure of 1 to 5atmospheres, and a leach time up to two hours.

An especially effective process, in terms of optimum radionuclideremoval for minimum cost, involves a sulphuric acid leach, preferably0.5 to 2M, more preferably 1 to 1.5M, followed by a pre-treatment with adilute alkali hydroxide solution, preferably sodium hydroxide solution,and then a hydrochloric acid leach, preferably 0.05 to 2M. The residueof the sulphuric acid leach is preferably washed, eg with water, beforethe pre-treatment, and further washes preferably occur after thepre-treatment and after the hydrochloric acid leach. The requiredconcentration of sodium hydroxide is dependent, inter alia, on theeffectiveness of the washing step, but a sodium hydroxide concentrationas low as 0.001M may be sufficient. The sodium hydroxide concentrationis preferably in the range from about 0.005 to 0.05M may suffice, morepreferably not above 0.1M, most preferably 0.005 to 0.01M. Duration ofthe pre-treatment is preferably at least 5 minutes and up to 60 minutes.Despite the multiple steps required in this process, the lowconcentrations of acid and sodium hydroxide make it overall costeffective, especially given that recycling of reagents can be avoided.

Our understanding of the process at this time, at least in relation tothe case where the impurities include thorium radionuclides and relateddaughter radionuclides including radium, is that the sulphuric aciddissolves thorium and other impurity elements including residual iron(primarily ferrous or ferric but some metallic), but not radium, fromthe aerated product and that the subsequent washing and sodium hydroxidetreatment remove sulphate salts (perhaps by deprotonation) from thesulphuric acid leach residue. These sulphate salts precipitate duringthe sulphuric acid leach. Removal of the sulphate salts is necessary sothat the sulphate levels in the hydrochloric acid leach remain as low aspossible in the leach solution, perhaps below a determinable criticallevel, for effectiveness of this leach. This requirement needs to bekept in mind in providing the leach solution for the hydrochloric acidleach: the sulphate concentration in this solution is preferablymaintained as low as possible, eg well below 50 ppm. The radium isthought to precipitate in the sulphuric acid leach as radium sulphate:this salt is not significantly removed in the sodium hydroxide treatmentbut is modified in a manner effective for it to be extracted during thehydrochloric acid leach, perhaps by the mechanism noted above.

For removing thorium and its radionuclide daughters, the hydrochloricacid leach is preferably limited to a time, determined by observation,beyond which radium removal in the leach is actually diminished. Thispreferred maximum time will vary according to other conditions but maytypically be in the range 10 to 30 minutes.

The invention is further described and illustrated in the followingnon-limiting examples. All assays reported, except for radium, weredetermined by x-ray fluorescence spectrometry. Gamma-spectrometry wasused to measure the ²²⁸ Ra content of the samples and this value isgiven as the radium assay in the examples. A lowering of the radiumassay indicates a lowering of the radioactivity level of the sample.

EXAMPLE 1

A comparison of the removal of thorium, radium and other impurities froman aerated product, derived from reduced ilmenite made with a boratemineral added during reduction, is made for different leaching systemsin this example.

Eneabba North ilmenite as feedstock, was reduced in accordance with theBecher process employing a commercial-size rotary reduction kilnmeasuring 27.4 m long, refractory lined to give an internal diameter of2.0 m. During the reduction a calcium borate mineral was added. Thereduced ilmenite produced was aerated in a 30 liter laboratory aeratorand the oxide produced was removed to obtain the aerated product whichwas leached.

Samples of the aerated product were leached with

(i) sulphuric acid (1.0M) at 40 wt % solids and 60° C. for 120 minutes,or

(ii) hydrochloric acid (1.0, 1.5 or 2.0M) at 40 wt % solids and 30° C.for 10 minutes, or

(iii) sulphuric acid (1.25M) at 40 wt % solids and 60° C. for 120minutes followed by treatment with sodium hydroxide (0.01M) at 40 wt %solids and 25° C. for 30 minutes and then leached with hydrochloric acid(0.2M) at 40 wt % solids and 30° C. for 10 minutes. Between each stepthe solids were washed with water.

The results in Table 1 show that a single leach with sulphuric acidremoves thorium and impurities such as calcium, iron, manganese, siliconand aluminium but does not remove radium, and so the activity of thesample is not lowered.

The results also show that a single leach with hydrochloric acid removesradium to a greater extent than sulphuric acid but the removal of theother impurities, in particular thorium, is not as efficient, even withan acid strength of 2.0M hydrochloric acid.

Leaching with sulphuric acid followed by a treatment with sodiumhydroxide and a leach with hydrochloric acid achieves the best removalof thorium, radium and the impurity elements. The advantage of thissystem over the single sulphuric acid or hydrochloric acid leaches isthat a higher quality product is obtained. Also, the lower hydrochloricacid concentration required after the sulphuric acid leach and sodiumhydroxide treatment means that this system is commercially economic andit is considered superior to the single leaching systems specified inthe International Patent Publication WO94/03647 (PCT/AU93/00381).

                                      TABLE 1                                     __________________________________________________________________________                 Th  Ra  CaO                                                                              Fe.sub.2 O.sub.3                                                                  Mn.sub.3 O.sub.4                                                                  SiO.sub.2                                                                        Al.sub.2 O.sub.3                           Treatment    (ppm)                                                                             (Bq/g)                                                                            (%)                                                                              (%) (%) (%)                                                                              (%)                                        __________________________________________________________________________    Aerated product                                                                            458 1.03                                                                              0.21                                                                             7.20                                                                              1.11                                                                              1.48                                                                             0.98                                       Leach with 1.0M H.sub.2 SO.sub.4                                                           63  1.07                                                                              0.02                                                                             2.12                                                                              0.71                                                                              1.01                                                                             0.50                                       Leach with 1.0M HCl                                                                        162 0.43                                                                              0.05                                                                             4.33                                                                              0.81                                                                              0.90                                                                             0.61                                       Leach with 1.5M HCl                                                                        129 0.40                                                                              0.05                                                                             3.72                                                                              0.80                                                                              0.87                                                                             0.57                                       Leach with 2.0M HC1                                                                        113 0.36                                                                              0.04                                                                             3.28                                                                              0.78                                                                              0.88                                                                             0.55                                       Leach with 1.25M H.sub.2 SO.sub.4                                                          55  0.98                                                                              0.02                                                                             1.96                                                                              0.75                                                                              0.94                                                                             0.48                                       Leach with 0.1M NaOH                                                                       55  n.d.                                                                              0.02                                                                             2.0O                                                                              0.75                                                                              0.78                                                                             0.47                                       Leach with 0.2M HC1                                                                        55  0.33                                                                              0.02                                                                             1.95                                                                              0.74                                                                              0.74                                                                             0.45                                       __________________________________________________________________________     n.d. = not determined                                                    

EXAMPLE 2

The beneficial effect of addition of a borate mineral during reductionof ilmenite on the subsequent removal of thorium and radium, and otherimpurities by leaching with sulphuric acid/sodium carbonate/hydrochloricacid is shown in this example.

Using Eneabba North ilmenite as feedstock, samples were reduced inaccordance with the Becher process employing a commercial-size rotaryreduction kiln measuring 27.4 m long, refractory lined to give aninternal diameter of 2.0 m. Two samples of reduced ilmenite (RI) wereprepared. One was prepared in the normal manner and can be considered asnormal run-of-plant RI. The other was produced under similar conditionsexcept that calcium borate as the mineral colemanite was added to thereduction kiln during the production of the RI. The reduced ilmenitesamples produced were aerated in the laboratory in a 2 liter glassreactor and the oxides produced were removed to obtain two aeratedproducts.

The aerated products were leached with sulphuric acid (0.5M) at 25 wt %solids and 60° C. for 60 minutes followed by treatment with sodiumcarbonate (0.1M) at 50 wt % solids and 80° C. for 60 minutes and then aleach with hydrochloric acid (0.2M) at 25 wt % solids and 60° C. for 60minutes. Between each step the solids were washed with water and dried.

The results in Table 2 indicate that both thorium and radium wereremoved from the aerated product from the reduced ilmenite sample thatcontained the borate mineral. However, very little thorium or radium,were removed from the normal run-of-plant sample. It can be seen thatsignificant amounts of iron, manganese, silicon, and aluminium were alsoremoved from the sample with the borate mineral added but not from thenormal run-of-plant sample.

                                      TABLE 2                                     __________________________________________________________________________                     Th  Ra  CaO                                                                              Fe.sub.2 O.sub.3                                                                  Mn.sub.3 O.sub.4                                                                  SiO.sub.2                                                                        Al.sub.2 O.sub.3                       Sample  Treatment                                                                              (ppm)                                                                             (Bq/g)                                                                            (%)                                                                              (%) (%) (%)                                                                              (%)                                    __________________________________________________________________________    No borate added                                                                       Reduced ilmenite                                                                       354 1.51                                                                              0.02                                                                             37.0                                                                              1.36                                                                              1.37                                                                             0.99                                           Aerated prodnct                                                                        452 1.77                                                                              0.02                                                                             5.49                                                                              1.64                                                                              1.77                                                                             1.22                                           Leach witn H.sub.2 SO.sub.4                                                            412 n.d.                                                                              0.02                                                                             5.07                                                                              1.58                                                                              1.72                                                                             1.19                                           Leach with Na.sub.2 CO.sub.3                                                           412 n.d.                                                                              0.02                                                                             5.07                                                                              1.57                                                                              1.70                                                                             1.17                                           Leach with HCl                                                                         403 1.72                                                                              0.02                                                                             4.96                                                                              1.56                                                                              1.70                                                                             1.19                                   Borate added                                                                          Reduced ilmenite                                                                       354 1.44                                                                              0.98                                                                             36.6                                                                              1.32                                                                              1.59                                                                             0.96                                           Aerated product                                                                        448 0.9 0.40                                                                             5.88                                                                              1.02                                                                              1.09                                                                             0.94                                           Leach with H.sub.2 SO.sub.4                                                            114 0.79                                                                              0.18                                                                             2.40                                                                              0.74                                                                              0.61                                                                             0.38                                           Leach with Na.sub.2 CO.sub.3                                                           n.d.                                                                              n.d.                                                                              n.d.                                                                             n.d.                                                                              n.d.                                                                              n.d.                                                                             n.d.                                           Leach with HCl                                                                         114 0.25                                                                              0.18                                                                             2.25                                                                              0.74                                                                              0.38                                                                             0.38                                   __________________________________________________________________________     n.d. = not determined                                                    

EXAMPLE 3

The beneficial effect of addition of a borate mineral during reductionof ilmenite on the subsequent removal of thorium and radium, and otherimpurities by leaching with sulphuric acid/sodium hydroxide/hydrochloricacid is shown in this example.

Samples of Eneabba North ilmenite were reduced in a similar manner toExample 2. The run-of-plant reduced ilmenite was aerated in thelaboratory in a 2 liter glass reactor and the oxides produced wereremoved to obtain an aerated product. The RI with the colemanite addedwas aerated in a 160 liter pilot plant aerator and the oxides producedwere removed to obtain the aerated product.

The aerated products were leached with sulphuric acid (1.6M) at 40 wt %solids and 60° C. for 60 or 120 minutes followed by treatment withsodium hydroxide (0.01M) at 40 wt % solids and 25° C. for 30 or 60minutes and then leached with hydrochloric acid (0.4M) at 40 wt % solidsand 60° C. for 60 minutes. Between each step the solids were washed withwater.

The results in Table 3 are similar to those for Example 2 in that boththorium and radium, and other impurities such as iron, manganese,silicon and aluminium, were removed from the aerated product from the RIsample that had the borate mineral added in reduction but littlethorium, radium or other impurities were removed from the normalrun-of-plant sample.

These results also indicate the products from the laboratory and pilotplant aerations of RI to which a borate mineral was added have similarleaching properties.

                                      TABLE 3                                     __________________________________________________________________________                     Th  Ra  CaO                                                                              Fe.sub.2 O.sub.3                                                                  Mn.sub.3 O.sub.4                                                                  SiO.sub.2                                                                        Al.sub.2 O.sub.3                       Sample  Treatment                                                                              (ppm)                                                                             (Bq/g)                                                                            (%)                                                                              (%) (%) (%)                                                                              (%)                                    __________________________________________________________________________    No borate added                                                                       Reduced ilmenite                                                                       383 1.62                                                                              0.08                                                                             34.5                                                                              1.14                                                                              1.50                                                                             0.98                                           Aerated product                                                                        459 1.92                                                                              0.08                                                                             4.79                                                                              1.32                                                                              1.81                                                                             1.21                                           Leach with H.sub.2 SO.sub.4                                                            377 n.d.                                                                              0.07                                                                             3.96                                                                              1.20                                                                              1.85                                                                             1.22                                           Leach with NaOH                                                                        361 n.d.                                                                              0.07                                                                             3.91                                                                              1.19                                                                              1.84                                                                             1.23                                           Leach with HCl                                                                         369 1.73                                                                              0.06                                                                             3.94                                                                              1.20                                                                              1.86                                                                             1.24                                   Borate added                                                                          Reduced ilmenite                                                                       354 1.44                                                                              0.98                                                                             36.6                                                                              1.32                                                                              1.59                                                                             0.96                                           Aerated product                                                                        465 1.0 0.52                                                                             8.26                                                                              1.07                                                                              1.17                                                                             0.90                                           Leach with H.sub.2 SO.sub.4                                                             96 n.d.                                                                              0.17                                                                             1.50                                                                              0.72                                                                              0.63                                                                             0.32                                           Leach with NaOH                                                                         87 n.d.                                                                              0.17                                                                             1.53                                                                              0.72                                                                              0.61                                                                             0.34                                           Leach with HCl                                                                          87 0.38                                                                              0.15                                                                             1.48                                                                              0.72                                                                              0.63                                                                             0.36                                   __________________________________________________________________________     n.d. = not determined                                                    

EXAMPLE 4

Results for leaching with sulphuric acid followed by hydrochloric acid,with and without a pre-treatment with sodium hydroxide before thehydrochloric acid leach are given in this example.

Eneabba North ilmenite as feedstock, was reduced in accordance with theBecher process employing a commercial-size rotary reduction kilnmeasuring 27.4 m long, refractory lined to give an internal diameter of2.0 m. During the reduction a calcium borate as the mineral colemanitewas added to the kiln. The reduced ilmenite produced was aerated in a160 liter pilot plant aerator and the oxide produced was removed toobtain the aerated product which was leached.

The aerated product was leached with sulphuric acid (2.0M) at 40 wt %solids and 60° C. for 60 minutes followed by a leach with hydrochloricacid (0.4M) at 40 wt % solids and 60° C. for 60 minutes. The solids werewashed with water between leaches.

A separate sample of the aerated product was also leached with sulphuricacid (1.6M) at 40 wt % solids and 60° C. for 60 minutes followed bytreatment with sodium hydroxide (0.01M) at 40 wt % solids and 25° C. for30 minutes and then a leach with hydrochloric acid (0.2M) at 40 wt %solids and 30° C. for 60 minutes. Between each step the solids werewashed with water and dried.

The results in Table 4 indicate that thorium and radium, and many of theother impurities in the sample (such as calcium, iron, manganese,silicon and aluminium), were removed from the aerated product by the twoleaching systems. However, with the sodium hydroxide treatment betweenthe two acid leaches, the removal of radium in the hydrochloric acid wasgreater.

                                      TABLE 4                                     __________________________________________________________________________              Th  Ra   CaO                                                                              Fe.sub.2 O.sub.3                                                                   Mn.sub.3 O.sub.4                                                                  SiO.sub.2                                                                         Al.sub.2 O.sub.3                           Treatment (ppm)                                                                             (Bq/g)                                                                             (%)                                                                              (%)  (%) (%) (%)                                        __________________________________________________________________________    Aerated product                                                                         465 1.0  0.52                                                                             8.26 1.07                                                                              1.27                                                                              0.96                                       Leach witb H.sub.2 SO.sub.4                                                             93  0.74 0.15                                                                             2.15 0.72                                                                              0.66                                                                              0.35                                       Leach with HCl                                                                          83  0.58 0.16                                                                             1.83 0.71                                                                              0.61                                                                              0.33                                       Aerated product                                                                         465 1.0  0.52                                                                             8.26 1.07                                                                              1.27                                                                              0.96                                       Leach with H.sub.2 SO.sub.4                                                             96  n.d. 0.17                                                                             1.50 0.72                                                                              0.63                                                                              0.32                                       NaOH treatment                                                                          87  n.d. 0.17                                                                             1.49 0.73                                                                              0.59                                                                              0.33                                       Leach with HCl                                                                          87  0.36 0.16                                                                             1.45 0.72                                                                              0.63                                                                              0.35                                       __________________________________________________________________________     n.d. = not determined                                                    

EXAMPLE 5

The effect of the addition of sodium chloride to the hydrochloric acidleach is illustrated in this example.

Using Eneabba North ilmenite as feedstock, aerated product was producedin a similar manner to Example 4.

A sample of the aerated product was leached with sulphuric acid (2M) at60 wt % solids and 60° C. for 60 minutes and then twice withhydrochloric acid (0.4M) containing sodium chloride (1M) at 40 wt %solids and 40° C. for 60 minutes.

As well, another sample of the aerated product was leached twice withhydrochloric acid (0.4M) containing sodium chloride (1M) at 40 wt %solids and 40° C. for 60 minutes, and then with sulphuric acid (2M) at60 wt % solids and 60° C. for 60 minutes.

The results in Table 5 show that good removal of thorium, radium andimpurities were achieved from the aerated product by both leachingroutes.

                                      TABLE 5                                     __________________________________________________________________________              Th   Ra  CaO Fe.sub.2 O.sub.3                                                                  Mn.sub.3 O.sub.4                                                                  SiO.sub.2                                                                         Al.sub.2 O.sub.3                           Treatment (ppm)                                                                              (Bq/g)                                                                            (%) (%) (%) (%) (%)                                        __________________________________________________________________________    Aerated product                                                                         465  1.0 0.52                                                                              8.26                                                                              1.07                                                                              1.27                                                                              0.96                                       Leach with H.sub.2 SO.sub.4                                                             143  n.d.                                                                              0.19                                                                              2.40                                                                              0.74                                                                              0.79                                                                              0.39                                       Leach with HCl/NaCl                                                                     97   0.9 0.16                                                                              1.74                                                                              0.73                                                                              0.73                                                                              0.36                                       Leach with HCl/NaCl                                                                     88   <0.3                                                                              0.18                                                                              1.84                                                                              0.73                                                                              0.68                                                                              0.35                                       Aerated product                                                                         465  1.0 0.52                                                                              8.26                                                                              1.07                                                                              1.17                                                                              0.90                                       Leach with HCl/NaCl                                                                     456  0.8 0.36                                                                              5.78                                                                              0.90                                                                              1.27                                                                              0.96                                       Leach with HCl/NaCl                                                                     474  0.4 0.22                                                                              4.18                                                                              0.78                                                                              1.20                                                                              0.59                                       Leach with H.sub.2 SO.sub.4                                                             95   0.3 0.17                                                                              1.57                                                                              0.73                                                                              1.16                                                                              0.36                                       __________________________________________________________________________     n.d. = not determined                                                    

EXAMPLE 6

The effect of adding borate minerals during reduction in a laboratoryfurnace is shown in this example.

Two samples of Eneabba North ilmenite were reduced with coal (-10+5 mm)in a rolling drum in a laboratory roller bed furnace at 1100° C. using aheating profile similar to that in commercial Becher reduction kiln toobtain a reduced ilmenite sample of similar composition to that obtainedin commercial plants. Different calcium borate minerals were added tothe respective samples before the reduction. The former borate alsocontained sodium and indeed was the sodium calcium borate mineralulexite. The reduced ilmenite samples produced were aerated in thelaboratory in a 2 liter glass reactor and the oxides produced wereremoved to obtain two aerated products.

The aerated products were leached with sulphuric acid (1.5M) at 40 wt %solids and 60° C. for 120 minutes followed by treatment with sodiumhydroxide (0.01M) at 40 wt % solids and 25° C. for 30 minutes and thenleached with hydrochloric acid (0.1 or 0.2M) at 40 wt % solids and 60°C. for 10 minutes. Between each step the solids were washed with water.

The results in Table 6 show that good removal of thorium, radium andother impurities were achieved from RI with these two borate mineralsadded in reduction. Also the low hydrochloric acid concentrations usedto achieve the final removal of impurities should be noted. Theseconcentrations are much lower than those specified in InternationalPatent Application WO94/03647 (PCT/AU93/00381).

                                      TABLE 6                                     __________________________________________________________________________                     Th  Ra  CaO                                                                              Fe.sub.2 O.sub.3                                                                  Mn.sub.3 O.sub.4                                                                  SiO.sub.2                                                                        Al.sub.2 O.sub.3                              Treatment (ppm)                                                                             (Bq/g)                                                                            (%)                                                                              (%) (%) (%)                                                                              (%)                                    __________________________________________________________________________    First Sample                                                                         Reduced ilmenite                                                                        375 1.34                                                                              0.45                                                                             36.2                                                                              1.12                                                                              2.07                                                                             1.15                                          Aerated product                                                                         405 1.25                                                                              0.23                                                                             4.39                                                                              1.08                                                                              2.05                                                                             1.39                                          Leach with H.sub.2 SO.sub.4                                                             101 1.29                                                                              0.02                                                                             0.96                                                                              0.40                                                                              1.86                                                                             0.75                                          Leach with NaOH                                                                         101 1.23                                                                              0.02                                                                             0.89                                                                              0.40                                                                              1.68                                                                             0.72                                          Leach with 0.1M HCl                                                                     109 0.37                                                                              0.02                                                                             0.93                                                                              0.40                                                                              1.64                                                                             0.73                                          Leach with 0.2M HCl                                                                     109 0.31                                                                              0.02                                                                             0.92                                                                              0.40                                                                              1.77                                                                             0.78                                   Second Sample                                                                        Reduced ilmenite                                                                        373 1.38                                                                              0.44                                                                             36.0                                                                              1.33                                                                              2.11                                                                             1.16                                          Aerated product                                                                         388 1.08                                                                              0.15                                                                             4.74                                                                              1.12                                                                              2.06                                                                             1.36                                          Leach with H.sub.2 SO.sub.4                                                             109 1.05                                                                              0.01                                                                             1.72                                                                              0.51                                                                              1.85                                                                             1.02                                          Leach with NaOH                                                                         109 1.02                                                                              0.02                                                                             1.68                                                                              0.52                                                                              1.84                                                                             1.04                                          Leach with 0.1M HCl                                                                     109 0.41                                                                              0.01                                                                             1.53                                                                              0.51                                                                              1.70                                                                             0.99                                          Leach with 0.2M HCl                                                                     109 0.36                                                                              0.01                                                                             1.53                                                                              0.50                                                                              1.77                                                                             1.08                                   __________________________________________________________________________

EXAMPLE 7

The effect of adding borate minerals to a commercial reduction kiln isshown in this example.

Eneabba North ilmenite as feedstock, was reduced in accordance with theBecher process employing a commercial-size rotary reduction kilnmeasuring 27.4 m long, refractory lined to give an internal diameter of2.0 m. During the reduction different calcium borate minerals, the sameas those employed in Example 6, were added to the kiln during successivetime periods. The reduced ilmenite produced during the first period wasaerated in a 160 liter pilot plant aerator, while the reduced ilmeniteproduced during the second period was aerated in a 30 liter laboratoryaerator. The oxide produced was removed to obtain the aerated productswhich were leached.

The aerated products were leached with sulphuric acid (1.6 or 1.25M,respectively) at 40 wt % solids and 60° C. for 60 minutes followed bytreatment with sodium hydroxide (0.01M) at 40 wt % solids and 25° C. for30 minutes and then leached with hydrochloric acid (0.2M) at 40 wt %solids and 60° C. for 10 minutes. Between each step the solids werewashed with water.

The results in Table 7 show that good removal of thorium, radium andother impurities was achieved from the RI samples with the two borateminerals added during reduction in a commercial kiln.

                                      TABLE 7                                     __________________________________________________________________________                    Th  Ra  CaO                                                                              Fe.sub.2 O.sub.3                                                                  Mn.sub.3 O.sub.4                                                                  SiO.sub.2                                                                        Al.sub.2 O.sub.3                               Treatment                                                                              (ppm)                                                                             (Bq/g)                                                                            (%)                                                                              (%) (%) (%)                                                                              (%)                                     __________________________________________________________________________    First Period                                                                         Aerated product                                                                        465 1.00                                                                              0.52                                                                             8.26                                                                              1.07                                                                              1.27                                                                             0.96                                           Leach with H.sub.2 SO.sub.4                                                            96  n.d.                                                                              0.17                                                                             1.50                                                                              0.72                                                                              0.63                                                                             0.32                                           Leach with NaOH                                                                        87  n.d.                                                                              0.17                                                                             1.49                                                                              0.73                                                                              0.59                                                                             0.33                                           Leach with HCl                                                                         87  0.28                                                                              0.16                                                                             1.55                                                                              0.73                                                                              0.64                                                                             0.36                                    Second Period                                                                        Aerated product                                                                        458 1.03                                                                              0.21                                                                             7.20                                                                              1.11                                                                              1.48                                                                             0.98                                           Leach with H.sub.2 SO.sub.4                                                            63  n.d.                                                                              0.01                                                                             1.90                                                                              0.74                                                                              0.97                                                                             0.51                                           Leach with NaOH                                                                        63  n.d.                                                                              0.02                                                                             1.83                                                                              0.74                                                                              0.87                                                                             0.48                                           Leach with HCl                                                                         63  0.20                                                                              0.01                                                                             1.80                                                                              0.73                                                                              0.83                                                                             0.48                                    __________________________________________________________________________     n.d. = not determined                                                    

EXAMPLE 8

The requirement for an excess sulphuric acid concentration to achievegood thorium removal is illustrated in this example.

Eneabba North ilmenite as feedstock, was reduced in accordance with theBecher process employing a commercial-size rotary reduction kilnmeasuring 27.4 m long, refractory lined to give an internal diameter of2.0 m. During the reduction a calcium borate mineral was added. Thereduced ilmenite produced was aerated in a 60 cubic meter plant aeratorand the oxide produced was removed to obtain the aerated product whichwas leached.

Samples of the aerated product were leached with sulphuric acid (0.6 or1.0M) at 40 wt % solids and 60° C. for 120 minutes followed by treatmentwith sodium hydroxide (0.03M) at 40 wt % solids and 25° C. for 30minutes and then leached with hydrochloric acid (0.1 or 0.4M) at 40 wt %solids and 60° C. for 5 or 30 minutes. Between each step the solids werewashed with water.

The results in Table 8 show that much less thorium was removed with 0.6Msulphuric acid compared with 1.0M sulphuric acid. The free acid levelsafter the leaches were 0.07M and 0.23M, respectively. This resultindicates that an excess sulphuric acid of at least 0.2M (20 g/Lsulphuric acid) is required to obtain a satisfactory removal of thoriumin the sulphuric acid leach. The concentration to be used depends on theimpurity levels in the aerated product, particularly the iron content.

The results in Table 8 also indicate that when insufficient sulphuricacid is used, a higher hydrochloric acid level is necessary for similarresults. The results show that a hydrochloric acid concentration of 0.1Mis sufficient to remove radium after a sulphuric acid leach with 0.2Macid excess.

                                      TABLE 8                                     __________________________________________________________________________                   Th  Ra  CaO                                                                              Fe.sub.2 O.sub.3                                                                  Mn.sub.3 O.sub.4                                                                  SiO.sub.2                                                                        Al.sub.2 O.sub.3                         Treatment      (ppm)                                                                             (Bg/g)                                                                            (%)                                                                              (%) (%) (%)                                                                              (%)                                      __________________________________________________________________________    Aerated product                                                                              447 0.97                                                                              0.20                                                                             8.55                                                                              1.36                                                                              1.24                                                                             0.95                                     Leach with 0.6M H.sub.2 SO.sub.4                                                             265 n.d.                                                                              0.02                                                                             3.94                                                                              0.86                                                                              0.82                                                                             0.51                                     Leach with NaOH                                                                              257 n.d.                                                                              0.03                                                                             3.91                                                                              0.86                                                                              0.70                                                                             0.48                                     Leach with 0.1M HCl for 5 min                                                                232 0.34                                                                              0.02                                                                             3.81                                                                              0.86                                                                              0.68                                                                             0.48                                     Aerated product                                                                              447 0.97                                                                              0.20                                                                             8.55                                                                              1.36                                                                              1.24                                                                             0.95                                     Leach with 0.6M H.sub.2 SO.sub.4                                                             249 n.d.                                                                              0.02                                                                             3.79                                                                              0.86                                                                              0.84                                                                             0.48                                     Leach with NaOH                                                                              249 n.d.                                                                              0.02                                                                             3.78                                                                              0.85                                                                              0.69                                                                             0.49                                     Leach with 0.4M HCl for 30 min                                                               133 0.27                                                                              0.02                                                                             3.61                                                                              0.85                                                                              0.64                                                                             0.45                                     Aerated product                                                                              447 0.97                                                                              0.20                                                                             8.55                                                                              1.36                                                                              1.24                                                                             0.95                                     Leach with 1.0M H.sub.2 SO.sub.4                                                             59  n.d.                                                                              0.02                                                                             2.68                                                                              0.85                                                                              0.75                                                                             0.43                                     Leach with NaOH                                                                              59  n.d.                                                                              0.02                                                                             2.53                                                                              0.84                                                                              0.48                                                                             0.43                                     Leach with 0.1M HCl for 30 min                                                               67  0.25                                                                              0.02                                                                             2.48                                                                              0.84                                                                              0.44                                                                             0.43                                     Aerated product                                                                              447 0.97                                                                              0.20                                                                             8.55                                                                              1.36                                                                              1.24                                                                             0.95                                     Leach with 1.0M H.sub.2 SO.sub.4                                                             67  n.d.                                                                              0.02                                                                             2.51                                                                              0.84                                                                              0.73                                                                             0.45                                     Leach witn NaOH                                                                              67  n.d.                                                                              0.02                                                                             2.50                                                                              0.85                                                                              0.49                                                                             0.42                                     Leach with 0.4M HCl for 5 min                                                                59  0.24                                                                              0.02                                                                             2.49                                                                              0.85                                                                              0.49                                                                             0.43                                     __________________________________________________________________________     n.d. = not determined                                                    

EXAMPLE 9

The effect of the hydrochloric acid leach time and the solids pulpdensity of the leaches on radium removal is shown in this example.

Eneabba North ilmenite as feedstock, was reduced in accordance with theBecher process employing a commercial-size rotary reduction kilnmeasuring 27.4 m long, refractory lined to give an internal diameter of2.0 m. During the reduction a calcium borate was added to the kilnduring each of two periods. The reduced ilmenite produced during thefirst period was aerated in a 160 liter pilot plant aerator, while thereduced ilmenite produced in the second period was aerated in a 60 cubicmeter plant aerator. The oxide produced was removed to obtain theaerated products which were leached.

The aerated product from RI from the first period was leached withsulphuric acid (1.6M) at 40 wt % solids and 60° C. for 60 minutesfollowed by treatment with sodium hydroxide (0.01M) at 40 wt % solidsand 25° C. for 30 minutes and then leached with hydrochloric acid (0.2M)at 40 wt % solids and 30° C. for 2, 5, 10, 60 and 120 minutes. Betweeneach step the solids were washed with water.

The aerated product from RI from the second period was leached at 15 wt% solids, instead of 40 wt % solids, with sulphuric acid (1.0M) at 60°C. for 120 minutes followed by treatment with sodium hydroxide (0.03M)at 25° C. for 30 minutes and then leached with hydrochloric acid (0.05M)at 30° C. for 10 and 120 minutes, and 24 hours. Between each step thesolids were washed with water. (0.05M hydrochloric acid was used so thatthe amount of acid to weight of solids was the same as for a 40 wt %solids leach.)

The results in Table 9 show that, for leaches at 40 wt % solids, theamount of radium removed in the hydrochloric acid leach was not as greatfor leach times of 60 minutes or longer. However, for leaches at lowersolids pulp density, this effect of time on radium removal was notevident.

                                      TABLE 9                                     __________________________________________________________________________                        Th  Ra  CaO                                                                              Fe.sub.2 O.sub.3                                                                  Mn.sub.3 O.sub.4                                                                  SiO.sub.2                                                                        Al.sub.2 O.sub.3                    Solids density                                                                       Treatment    (ppm)                                                                             (Bq/g)                                                                            (%)                                                                              (%) (%) (%)                                                                              (%)                                 __________________________________________________________________________    40 wt % solids                                                                       Aerated Product                                                                            465 1.00                                                                              0.52                                                                             8.26                                                                              1.07                                                                              1.27                                                                             0.96                                       Leach with H.sub.2 SO.sub.4                                                                96  n.d.                                                                              0.17                                                                             1.50                                                                              0.72                                                                              0.63                                                                             0.32                                       Leach with NaOH                                                                            87  n.d.                                                                              0.17                                                                             1.49                                                                              0.73                                                                              0.59                                                                             0.33                                       Leach with HCl for 2 min                                                                   87  0.31                                                                              0.16                                                                             1.46                                                                              0.72                                                                              0.59                                                                             0.35                                       Leach with HCl for 5 min                                                                   87  0.30                                                                              0.16                                                                             1.54                                                                              0.72                                                                              0.60                                                                             0.35                                       Leach with HCl for 10 min                                                                  87  0.28                                                                              0.16                                                                             1.55                                                                              0.73                                                                              0.64                                                                             0.36                                       Leach with HCl for 60 min                                                                  87  0.36                                                                              0.16                                                                             1.45                                                                              0.72                                                                              0.63                                                                             0.35                                       Leach with HCl for 120 min                                                                 87  0.40                                                                              0.16                                                                             1.47                                                                              0.71                                                                              0.58                                                                             0.35                                15 wt % solids                                                                       Aerated product                                                                            447 0.97                                                                              0.20                                                                             8.55                                                                              1.36                                                                              1.24                                                                             0.95                                       Leach with H.sub.2 SO.sub.4                                                                72  n.d.                                                                              0.02                                                                             2.75                                                                              0.84                                                                              0.75                                                                             0.44                                       Leach with NaOH                                                                            64  n.d.                                                                              0.02                                                                             2.53                                                                              0.80                                                                              0.48                                                                             0.43                                       Leach with HCl for 10 min                                                                  56  0.23                                                                              0.02                                                                             2.55                                                                              0.82                                                                              0.51                                                                             0.47                                       Leach with HCl for 120 min                                                                 64  0.22                                                                              0.02                                                                             2.57                                                                              0.83                                                                              0.50                                                                             0.45                                       Leach with HCl for 24 hours                                                                64  0.21                                                                              0.02                                                                             2.29                                                                              0.81                                                                              0.54                                                                             0.46                                __________________________________________________________________________     n.d. = not determined                                                    

EXAMPLE 10

The detrimental effect of sulphate ions in the hydrochloric acid leachon radium removal is shown in this example. In practice the impuritysulphate ions may be present as a result of inefficient washing afterthe sulphuric acid leach or the sodium hydroxide treatment or be presentin the water used to make up the hydrochloric acid.

Using Eneabba North ilmenite as feedstock, an aerated product wasproduced in a similar manner to Example 1.

Samples of the aerated product from RI were leached with sulphuric acid(1.25M) at 40 wt % solids and 60° C. for 120 minutes followed bytreatment with sodium hydroxide (0.01M) at 40 wt % solids and 25° C. for30 minutes and then leached with hydrochloric acid (0.2M) at 40 wt %solids and 30° C. for 10, or 30 minutes. The hydrochloric acid leacheswere carried out with additions of sodium sulphate corresponding to 0,50 or 100 ppm SO₄ in the leach liquor. Between each step the solids werewashed with water.

The results in Table 10 clearly show the poorer radium removal whensulphate ions are present in the hydrochloric acid leach. The resultsalso indicate that a hydrochloric leaching time of up to 30 minutes isadvantageous.

                                      TABLE 10                                    __________________________________________________________________________                       Th  Ra  CaO                                                                              Fe.sub.2 O.sub.3                                                                  Mn.sub.3 O.sub.4                                                                  SiO.sub.2                                                                        Al.sub.2 O.sub.3                     Sulphate added                                                                       Treatment   (ppm)                                                                             (Bq/g)                                                                            (%)                                                                              (%) (%) (%)                                                                              (%)                                  __________________________________________________________________________           Aerated Product                                                                           458 1.03                                                                              0.21                                                                             7.20                                                                              1.11                                                                              1.48                                                                             0.98                                        Leach with H.sub.2 SO.sub.4                                                               63  1.07                                                                              0.01                                                                             1.90                                                                              0.74                                                                              0.97                                                                             0.51                                        Leach with NaOH                                                                           63  n.d.                                                                              0.02                                                                             1.83                                                                              0.74                                                                              0.87                                                                             0.48                                 100 ppm SO.sub.4                                                                     Leach with HCl for 10 min                                                                 63  0.79                                                                              0.01                                                                             1.80                                                                              0.73                                                                              0.83                                                                             0.48                                 50 ppm SO.sub.4                                                                      Leach with HCl for 10 min                                                                 55  0.63                                                                              0.02                                                                             1.83                                                                              0.73                                                                              0.86                                                                             0.48                                 0 ppm SO.sub.4                                                                       Leach with HCl for 10 min                                                                 55  0.20                                                                              0.01                                                                             1.82                                                                              0.74                                                                              0.83                                                                             0.48                                        Aerated product                                                                           458 1.03                                                                              0.21                                                                             7.20                                                                              1.11                                                                              1.48                                                                             0.98                                        Leach with H.sub.2 SO.sub.4                                                               55  1.07                                                                              0.02                                                                             2.07                                                                              0.73                                                                              0.94                                                                             0.46                                        Leach with NaOH                                                                           55  n.d.                                                                              0.02                                                                             1.93                                                                              0.75                                                                              0.83                                                                             0.48                                 100 ppm SO.sub.4                                                                     Leach with HCl for 30 min                                                                 55  1.15                                                                              0.01                                                                             1.86                                                                              0.73                                                                              0.81                                                                             0.47                                 50 ppm SO.sub.4                                                                      Leach with HCl for 30 min                                                                 55  0.86                                                                              0.01                                                                             1.81                                                                              0.74                                                                              0.80                                                                             0.47                                 0 ppm SO.sub.4                                                                       Leach with HCl for 30 min                                                                 55  0.28                                                                              0.01                                                                             1.90                                                                              0.73                                                                              0.78                                                                             0.47                                 __________________________________________________________________________     n.d. = not determined                                                    

Throughout this specification and the claims which follow, unless thecontext requires otherwise, the word "comprise", or variations such as"comprises" or "comprising", will be understood to imply the inclusionof a stated integer or group of integers but not the exclusion of anyother integer or group of integers.

We claim:
 1. In a process for removing one or more radionuclidesincluding one or more radionuclide decay products from titaniferousmaterial, said material(i) being an aerated product or synthetic rutile,and (ii) containing said radionuclides in a form which is highly solublein acid,the process comprising leaching said material in a step-wisemanner with sulphuric acid solution and with hydrochloric acid solutionin either order, the improvement wherein the hydrochloric acid leach isenhanced for removal of one or more of said radionuclide decay productsby pre-treatment of said material with a solution of an effective amountof a hydroxide.
 2. The process of claim 1, wherein the radionuclidedecay products include radium.
 3. In a process for removing one or moreradionuclides and daughters thereof from titaniferous material, saidmaterial(i) being an aerated product or a synthetic rutile, and (ii)containing the radionuclides and in a phase which is highly soluble inacid, said phase being formed by contacting the titaniferous material atan elevated temperature with one or more reagents selected to form thephase at the elevated temperature, and which phase disperses onto thesurfaces of the titaniferous material and incorporates the radionuclidesand daughters thereof,the process comprising leaching said material in astep-wise manner with sulphuric acid solution and with hydrochloric acidsolution in either order, the improvement wherein the hydrochloric acidleach is enhanced for removal of one or more of said daughters bypre-treatment of said material with a solution of an effective amount ofan alkaline metal hydroxide at a concentration no greater than about0.1M, the temperature in the range ambient to about 80° C., and apressure in the range from about 1 to about 5 atmospheres.
 4. Theprocess of claim 3, wherein the daughters include radium.
 5. The processof claim 1, wherein the leach with sulphuric acid solution precedes theleach with hydrochloric acid solution.
 6. The process of claim 3,wherein the leach with sulphuric acid solution precedes the leach withhydrochloric acid solution.
 7. In a process for removing one or moreradionuclide decay products from titaniferous material, said material(i)being an aerated product or synthetic rutile, and (ii) containing saidradionuclide decay products in a form which is highly soluble inacid,the process comprising leaching said material in a step-wisemanner, with sulphuric acid solution and with hydrochloric acidsolution, the improvement wherein the hydrochloric acid leach isaugmented by pre-treatment of said material with a solution of aneffective amount of a hydroxide thereby to modify, and facilitateremoval by hydrochloric acid leaching of, sulphate salts of the decayproducts, which salts are formed during the sulphuric acid leach.
 8. Ina process for removing radium from titaniferous material, saidmaterial(i) being an aerated product or synthetic rutile, and (ii)containing said radium in a form which is highly soluble in acid,theprocess comprising leaching said material in a step-wise manner withsulphuric acid solution and with hydrochloric acid solution, theimprovement wherein the hydrochloric acid leach is augmented bypre-treatment of said material with a solution of an effective amount ofa hydroxide thereby to modify, and facilitate removal by hydrochloricacid leaching of, radium sulphate salts formed during the sulphuric acidleach.
 9. A process according to claim 1 wherein the products of eachleach and of the augmenting treatment are washed before the next step.10. A process according to claim 1 wherein the form of the radionuclideswhich is highly soluble in acid is a phase in which the radionuclideshave been incorporated.
 11. A process according to claim 10 wherein saidphase is a phase formed by contacting a titaniferous material at anelevated temperature with one or more reagents selected to form thephase at the elevated temperature, which phase disperses onto thesurfaces of the titaniferous material and incorporates theradionuclides.
 12. A process according to claim 11 wherein saidcontacting at an elevated temperature is during reduction of iron in thetitaniferous material.
 13. A process according to claim 11 wherein saidreagents include glass forming reagents.
 14. A process according toclaim 13 wherein the reagent is selected from alkali metal and alkalineearth metal borates.
 15. A process according to claim 11 wherein saidelevated temperature is in the range from about 900° C. to about 1200°C.
 16. A process according to claim 15 wherein said elevated temperatureis in the range from about 1050° C. to about 1200° C.
 17. A processaccording to claim 1 wherein the concentrations of the reagents areselected from the following, as appropriate, with reference to anaqueous solution which is contacted with the titaniferous material:sulphuric acid 0.1M to 5M; hydrochloric acid 0.01 to 3M; sodiumhydroxide 0.001 to 10M.
 18. A process according to claim 1 wherein theradionuclides include thorium and/or uranium and one or more of theirradionuclide daughters including radium.
 19. A process according toclaim 18, wherein the radionuclide is ²³² Th and the daughters include²²⁸ Th and 228Ra.
 20. A process according to claim 18 comprising asulphuric acid leach for removal of thorium, uranium and optionally oneor more non-radionuclide impurities, followed by a pre-treatment with adilute alkali hydroxide solution to treat residual sulphates and then ahydrochloric acid leach for removal of radium.
 21. A process accordingto claim 20 wherein the concentration of sodium hydroxide is no greaterthan about 0.1M, the temperature of the NaOH solution during saidpre-treatment is in the range ambient to about 90° C., and the pressureis in the range from about 1 to about 5 atmospheres.
 22. A processaccording to claim 20 wherein the concentration of sodium hydroxide isin the range from about 0.005 to about 0.01M.
 23. A process according toclaim 20, wherein the hydrochloric acid leach is for a period limited soas to optimise radium removal.
 24. A process according to claim 23wherein the period is a maximum of about 30 minutes.
 25. A processaccording to claim 20 wherein the alkali hydroxide pre-treatment, andany subsequent wash, and the hydrochloric acid solution are controlledto minimise the concentration of sulphate ions in the latter during thehydrochloric acid leach, effective to optimise radium removal.
 26. Aprocess according to claim 1 wherein the titaniferous material isselected from the group including ilmenite, altered ilmenite, reducedilmenite and synthetic rutile.
 27. A process according to claim 1wherein said titaniferous material is synthetic rutile in the form ofaerated product formed by treatment of ilmenite, which treatmentincludes reduction of iron therein largely to metallic iron and thenaqueous oxidation of the metallic iron to form a separable iron oxide.28. A process according to claim 1 wherein impurities comprising one ormore of the group consisting of silicon and/or silica, aluminum and/oralumina, manganese, residual iron and calcium are also removed.
 29. Aprocess according to claim 3 wherein the concentration of alkali metalhydroxide is in the range from about 0.005 to about 0.01M.
 30. A processaccording to claim 3 wherein the products of each leach and of theaugmenting treatment are washed before the next step.
 31. A processaccording to claim 3 wherein the titaniferous material is selected fromthe group including ilmenite, altered ilmenite, reduced ilmenite andsynthetic rutile.
 32. A process according to claim 3 wherein saidcontacting at an elevated temperature is during reduction of iron in thetitaniferous material.
 33. A process according to claim 32 wherein saidtitaniferous material is synthetic rutile in the form of aerated productformed by treatment of ilmenite, which treatment includes said reductionof iron therein largely to metallic iron and then aqueous oxidation ofthe metallic iron to form a separable iron oxide.
 34. A processaccording to claim 32 wherein said reagents include glass formingreagents.
 35. A process according to claim 34 wherein the reagent isselected from alkali metal and alkaline earth metal borates.
 36. Aprocess according to claim 3 wherein said elevated temperature is in therange from about 900° C. to about 1200° C.
 37. A process according toclaim 36 wherein said elevated temperature is in the range from about1050° C. to about 1200° C.
 38. A process according to claim 3 whereinsaid alkali metal hydroxide is sodium hydroxide.
 39. A process accordingto claim 3 wherein the radionuclide is ²³² Th and the daughters include²²⁸ TH and ²²⁸ Ra.